The invention concerns an optical switching element according to the preamble of claim 1. Furthermore, the invention concerns a switching arrangement according to the preamble of claim 3O. Such a switching arrangement is known from the IEEE Transactions on Components, Packaging, and Manufacturing Technologyxe2x80x94Part B, Vol. 1B, No. 2, May 1995, pp. 241-244.
Matrix switches are familiar for connecting of fiber-optics lines by which N optical input channels can be switched to M optical output channels in any desired way. The number of the optical fibers being switched depends on the particular application. In the realm of telecommunications, matrix switches with a plurality of input and output channels find use.
There are known mechanical matrix switches in which mirrors or prisms are moved with high precision. Switches based on mirror or prism arrangements require a very stable and precise construction. The required precision generally entails high technical expense.
Besides the optical switching elements the microoptical components of which are moved with high precision, there are also known optical switching elements which work by a switching principle that does not require a movement of microoptical.
GB 1 494 150 describes an optical switching element in an optical waveguide wherein one boundary surface on which the incident light impinges is switched between a condition of total reflection and transmission. The known optical switch has a narrow slit in the core of the optical waveguide. The slit forms a regular boundary surface between an optically more dense medium, i.e., the material of the core of the optical waveguide, and an optically less dense medium, i.e., a gaseous substance in the slit, so that light impinging on the boundary surface at a slant and conducted along the optical waveguide is totally reflected at the boundary surface in the direction of an adjoining optical waveguide. In order to switch to the transmitting condition, in which the light impinging on the boundary surface maintains its direction of propagation, a fluid is introduced into the slit, the index of refraction of which corresponds to the index of refraction of the material from which the core of the optical waveguide is made. The device provided for optional introducing of the substance into its fluid or gaseous phase is a storage vessel with a heating device arranged on the optical waveguide. By thermal expansion, the fluid is forced into the slit protruding through the cladding layer into the core layer of the optical waveguide. In another configuration, the fluid substance located in the slit is brought into the gas phase by heating.
The costly production of the familiar switch is a disadvantage, since it is first necessary to make a slit in an optical waveguide, affix a device for filling to it, and seal off this construction against the outside. Because of slitting the optical waveguide, it is only possible to realize parallel surfaces, and moreover these reflecting surfaces do not have high optical quality. Furthermore, the known switch has a high optical damping, since the light beam emerging from the optical waveguide in the region of the slit is divergent and not guided. Therefore, in the transmitting condition of the switch, a portion can be coupled over to the adjoining optical waveguide, which leads to considerable cross-talk in the familiar switch.
The basic purpose of the invention is to create an optical switching element with low optical damping and low cross-talk, which has a compact construction and a long lifetime, yet which is economical to produce. Furthermore, the purpose of the invention is to provide a switching arrangement with N optical inputs and M optical outputs with the aforementioned properties.
The purposes of the invention are achieved by the features indicated in Patent claim 1 and 30.
The optical switching element is characterized in that the recess contains a fluid and a body which can move in the recess, the fluid being of such nature and the movable body being of such configuration and able to move in the recess between a position in which the optical switching element is in the transmitting condition and a position in which the optical switching element is in a reflecting condition, that, in the transmitting condition of the switch, the region of the slit between the boundary surface and the surface of the movable body lying in the path of the incident light is filled completely with the fluid and, in the reflecting condition of the switch, at least the region of the boundary surface lying in the path of the incident light is free of the fluid, so that the incident light is essentially reflected at the boundary surface and at least one activating device is provided for switching the moveable body between the transmitting and the reflecting condition of the switch.
In the optical switching element according to the invention, the recess in the transparent base body is only partly filled with the fluid, which is extensively adapted to the index of refraction of the base body. For the switching between the transmitting and reflecting condition, a body which can move in the recess is provided. The movable body is configured such, and it can move in the recess between two positions, that in the transmitting condition of the switch at least the region of the slit lying in the path of the incident light between the boundary surface and the surface of the movable body is completely filled with the fluid. This ensures that the incident light is not totally reflected at the boundary surface, but rather passes through the boundary surface. In the reflecting condition, the body is situated in a position in which the boundary surface is free of fluid, so that the incident light is totally reflected at the boundary surface between the optically more dense medium, i.e., the material of the base body, and the optically less dense medium, i.e., a gas located in the cavity.
The decisive advantage of the switching element is that the boundary surface responsible for the switching process is not moved. Thanks to the preferential use of collimated light beams, no complicated waveguide structures are necessary for guiding the beam in the base body. Since the beam is not divergent, even in the recesses involved in the switching process, the optical multiple switch according to the invention has low optical damping and low cross-talk.
The use of the terms optical input and optical output in contrast with the term optical channel serves only to simplify the description of the optical switching element and its switching arrangements. Because the light paths are reversible, a use in both beam directions, i.e., bidirectional, is possible.
Preferably, the optical switching element according to the invention is operated with free beams, i.e., with light beams not traveling in waveguide structures. This can be achieved, for example, by collimating the light furnished by means of optical waveguides before it enters the switch proper. Basically, however, it is also conceivable to have optical structures for light guidance integrated in the optical switching element, e.g., by means of layer or groove waveguide structures, although this requires a more complex construction of the base body.
When the switching element is switched to the reflecting condition, the fluid must be completely retracted from the boundary surface in the shortest possible time. This effect can be supported in that the surfaces of the boundary involved in the switching condition are subjected to an additional treatment, such as chemical or plasma-chemical, or they are coated with one or more suitable materials. In this regard, a fine structuring of the relevant surfaces is also of advantage.
The base body and the body which can move in the recess consist at least in parts of materials which are transparent in the wavelength region used. If both bodies consist of the same material, this has the advantage that the bodies will have the same index of refraction. The fluid should likewise have a similar index of refraction.
The base body and the movable body can consist of transparent materials, like (fluorinated) polymers with low optical absorption in the desired spectral region, glasses, materials produced by sol-gel processes, silver halides. Conventional PMMA can be used for signal transmission in the visible region. In the infrared spectrum, modified polymers are advantageous.
Hybrid systems of different substances can also be used as the fluid. An adaptation of the index of refraction, e.g., for PMMA in the visual region, can be achieved by a mixture of decaline and tetraline.
A gas or a gas mixture can be used as the optically less dense medium. Suitable for this is an inert gas like argon. Advantageously, the gas has poor diffusion properties. But air is also suitable as the optically less dense medium.
It is of special advantage that the activating device for switching the movable body between the transmitting and the reflecting condition can be arranged outside the beam path. Since the actual switching process occurs through the fluid, an exact guidance of the movable body is not necessary, so that the activating device can be realized cheaply without major technical expense.
In theory, a direct mechanical coupling between the, e.g., piezoelectrical or thermoelectrical activating device and the movable body is possible. Preferably, however, the activating of the movable body is without contact, so that the recess can be hermetically encapsulated, which makes the switching element largely insensitive to external influences.
In a preferred embodiment, the activating device has an electromagnet arranged outside the recess, and the movable body is magnetic. Preferably, the movable body consisting of the same (nonmagnetic) material as the base body is provided with a layer on its surface or a body of a magnetic or a magnetizable material. Stable switching conditions independent of the power supply can be achieved with permanent magnets. In place of an electromagnetic activating device, an electrostatic activating device can also be provided. In a further embodiment, two activating devices arranged on opposite sides outside the recess are provided.
The fluid can be distributed in the recess by displacing the fluid with the movable body and forcing it into the slit. For this, the recess is filled so much with the fluid that, in the reflecting condition, the region of the boundary lying in the beam path of the incident light is outside the level of the fluid. In the transmitting condition, the movable body is moved into the fluid such that the region of the slit lying in the beam path of the incident light is filled with fluid by displacement. The fluid can be bound to the bottom of the recess, for example, with a spongelike material, so that the switching element functions independent of position.
In an alternative embodiment, a fluid film is formed between the movable body and the wall of the recess by means of capillary forces and it is carried along with the body during the switching process. Thus, in the transmitting condition, at least the region of the slit between the boundary surface and the surface of the movable body that lies in the beam path of the incident light is filled with the fluid film. In the reflecting condition, on the other hand, the region of the boundary surface lying in the beam path of the incident light is free of the fluid film. The two principles of displacement and of fluid film can also be combined.
The recess can essentially have any desired configuration. What is important is that the boundary surface be oriented to the direction of propagation of the incident light. The angle between the direction of propagation of the incident light and the boundary surface is not necessarily in the region of 40xc2x0 to 50xc2x0. Thus, it is conceivable to have the angle of incidence such that total reflection does not occur. With such an arrangement, the switching element could also be used as a beam splitter. However, it is preferably dimensioned such that a total reflection occurs.
In order that the air inside the recess not hinder the switching mechanism, for example, it is possible to provide venting slits at the margin of the recess. Through these channels, the optically less dense medium can then flow unhindered during the switching process. In another configuration, the movable body can have a corresponding suitable shape.
At least one lateral surface of the recess forms a light exit surface for the transmitted light. It is not necessary for the lateral surfaces not involved in the reflection to have the same surface quality as the lateral surfaces which form the boundary surface, inasmuch as these lateral surfaces not involved in the reflection are wetted with the fluid in the transmitting condition.
In one embodiment, the recess has a triangular cross section in the plane of the path of a light beam. In another embodiment, the recess has a rectangular cross section. Advantageously, the movable body essentially has the same cross section geometry as the recess. But it is also conceivable that at least one of the surfaces of the recess that reflects incident light beams as a boundary surface in the reflecting condition be shaped and arranged such that it focuses at least a portion of the light beams impinging on this surface during the reflecting.
The base body can advantageously have other recesses, which serve to accommodate and hold optical waveguides, for example, glass or plastic fibers or bands of fibers and fiber connectors. For example, these can be channel-like structures, each of which is open at one outer side of the base body, so that optical waveguides can be easily inserted into the base body in a defined position. Additional clamplike or springlike structures can be provided for fixation of the optical waveguides.
Furthermore, one or more recesses to accommodate optical elements can be provided in the base body. These are generally required to guide the light, because of the relatively high divergence of the light beams emerging from the input optical waveguides. Optical elements for collimating and/or focusing the light can be integrated in the base body, for example, spherical lenses, micro lenses, GRIN lenses, cylindrical lenses, etc. It is also conceivable to have, for example, cell-like micro lens fields to focus the light beams of several optical channels. Yet it is also possible to efficiently guide the light inside the base body with integrated optical waveguides, e.g., groove waveguides or film waveguides.
Yet it is also possible to arrange one or more additional recesses in the beam path that are shaped such as to focus incident light. Besides the shape of the recess, it is also the index of refraction of the substance or mixture of substances contained in the recess that is critical.
According to the invention, a light beam impinging on a boundary surface that is formed by a surface of the recess is reflected in the reflecting condition. The reflected beam impinges on one exit, whereas in the transmitting condition the beam passes through the recess and impinges on a different exit. Yet it is also conceivable to have several incident light beams impinging on the same boundary surface formed by a surface of the recess. Accordingly, several exits are to be provided for this.
In another embodiment of the invention, at least two incident light beams impinge on two boundary surfaces, which correspond to two surfaces of the recess. Advantageously, the light beams impinging on the two boundary surfaces lie at an angle of 70 to 110xc2x0 to each other. Preferably, in the transmitting condition, the light beam passing through the one boundary surface impinges on the same exit as the other light beam in the reflecting condition when it is reflected by the other boundary surface. The two lateral surfaces of the recess forming the boundary surfaces are roughly parallel to each other in one embodiment version. In a second embodiment version, these two surfaces of the recess make an angle of 70 to 110xc2x0, preferably around 90xc2x0. However, other geometries are also conceivable.
Preferably, in this second version, one cross section of the recess and of the movable body corresponds to an equilateral triangle in the plane of the path of a light beam. Such an arrangement in the case of two incident light beams preferably has three exits, and one exit corresponds to both a transmitted and also to another reflected light beam.
If this arrangement should only have two exits, then two additional reflecting surfaces need to be provided, at which the one transmitted light beam is reflected, preferably totally reflected, so that it impinges on the exit where another reflected light beam impinges in the reflecting condition. These two additional surfaces preferably form an angle of 70 to 110xc2x0 with each other. In a first embodiment, these two surfaces are formed by two outer surfaces of the base body. In a second embodiment, these two surfaces are formed by at least one additional recess, preferably filled with an optically less dense substance or mixture of substances. In a third embodiment, these two surfaces correspond to two surfaces of the movable body that are not wetted with fluid in the transmitting condition of the switch. In this case, the movable body has a preferably square cross section in the plane of the path of a light beam. Whereas in the other embodiments it is only necessary to have an exact position of the boundary surface formed by one or more lateral surfaces of the recess and the guiding of the movable body does not require high precision, it is necessary in this sample embodiment to establish the position of the movable body as precisely as possible in the transmitting condition of the switch.
In another embodiment of the invention, there are more than two optionally transmitting or reflecting boundary surfaces that are formed by correspondingly many surfaces of the recess. The recess and the movable body have, for example, a square cross section, which enables four boundary surfaces. Preferably, one reflected beam and one transmitted beam each impinge on the same exit in different conditions of the switch.
In the embodiments described thus far, more than one light beam can also be optionally reflected or transmitted at the boundary surface or the boundary surfaces. Basically, two arrangements or combinations of these two arrangements are conceivable here. According to the first arrangement, the incident light beams lie essentially in the same plane as their components which are reflected in the reflecting condition of the switch. According to the second arrangement, the plane of the incident light beams lies preferably at an angle of 70xc2x0 to 110xc2x0 to the plane of their reflected components.
In order to avoid the need to move the movable body across the entire range of the boundary surface lying in the beam path when there are several light beams impinging on one boundary surface, it may be advantageous for the movable body to have two regions of different cross section parallel to the plane of the beam path of one light beam. The regions of larger cross section advantageously lie so close to at least one surface of the recess that a fluid film can be maintained between these regions and the corresponding surface of the recess. The regions of smaller cross section lying between the regions of larger cross section preferably have such a distance from the corresponding surface of the recess that no fluid film can form in between. In order to get from the transmitting to the reflecting condition of the switch, the movable body only needs to be shifted enough that, instead of the regions with larger cross section, the nearest regions of smaller cross section of the movable body border on the regions of the boundary surface lying in the beam path.
The switch arrangement is characterized in that the recess contains the fluid and a movable body, the fluid being of such nature and the movable body of such configuration, and being so movable in the recess between one position in which the optical switching element is in the transmitting condition and another position in which the optical switching element is in the reflecting condition, that at least the region of a slit between the boundary surface and the surface of the movable body lying in the beam path of the incident light is completely filled with the fluid in the transmitting condition of the switch, and in the reflecting condition at least the portion of the boundary surface lying in the beam path of the incident light is free of the fluid, so that the incident light is essentially reflected at the boundary surface, and the at least one activating device serves to switch the switching element between the transmitting and the reflecting condition by moving the movable body.
All of the embodiments described above can be used as the switching element. The number of inputs and outputs can be the same or different (N=M or Nxe2x89xa0M).
In an expanded embodiment, besides the N optical inputs and M optical outputs there are additional N optical outputs, which are arranged on the side of the switch arrangement opposite the first N optical inputs. Furthermore, the possibility also exists to provide additional M optical inputs, which are arranged on the side of the switch arrangement opposite the first M optical outputs. Furthermore, the possibility also exists to provide 2xc3x97N optical inputs and 2xc3x97M optical outputs with Nxc3x97M optical switching elements in matrix arrangement.
If one particular input of the N input channels is to be switched to only the corresponding output of either the first N output channels or the second N output channels, a switch arrangement can also be feasible in which the N switching elements are arranged in the manner of a diagonal of a Nxc3x97N matrix.
The light can be guided into and out of the switch arrangement by means of optical waveguides. To couple the optical waveguides of the switching elements, there are N parallel channels, for example in the common base body, to accommodate the N input waveguides and M parallel channels to accommodate the M output waveguides, while the input channels for purposes of a simple geometrical construction are arranged at an angle of 70 to 110xc2x0 to the output channels and the boundary surfaces of the recesses of the individual switching elements are at an angle of 40 to 50xc2x0 to the input and output channels. The base body advantageously consists of a bottom plate, a structurized plate, and a top plate. For collimation/focusing of the light, it can be advantageous to integrate optical elements, especially micro lenses or GRIN lenses. For this, corresponding depressions are provided in the beam path between the input and output channels and the recesses of the switching elements.
In another embodiment, the individual switching elements are realized as self-standing switching modules, which can be used in a matrix plate with corresponding recesses arranged, for example, in the manner of a matrix. The matrix plate is advantageously provided with additional recesses suitable for accommodation of optical waveguides and/or optical components. With this modular construction, it is possible to advantageously provide and reconfigure flexible switching arrangements made from identical or different switch modules.
At least parts of the base body, the movable body, the activating device and/or the matrix plate can advantageously be produced with microtechnology methods, for example, by means of the LIGA process, in large numbers at favorable cost.
The optical switching elements described here and their switch arrangements can be used with particular advantage in the field of optical communications, especially for the arbitrary connecting or decoupling of optical communication channels and for the coupling of optical components into existing optical connections. Thanks to the possibility of arranging the reflected light beams perpendicular to the transmitted ones, compact optical bus systems can be realized with the switching elements and their switch arrangements according to the invention, similar to the bus systems familiar in microelectronics with plug-in cards and plates arranged at right angles.
Hereafter, several sample embodiments of the invention shall be explained more closely with reference to the drawings.